Accurate, yet inexpensive, distance measurements can be provided by an ultrasonic radar system that combines a piezoelectric transducer with a transducer controller. The controller may employ the piezoelectric transducer as both a transmitter and receiver of acoustic pulses, as this configuration typically reduces system complexity and cost. When operated as a transmitter, however, the transducer acts as resonator which is prone to self-oscillation (“reverberation”) for some time after the end of each transmitted pulse. The amplitude of vibration during the transmission phase (and for much of the reverberation phase) is orders of magnitude greater than the typical amplitude of a received echo, which causes the receiver portion of the controller to be saturated and unable to detect any echo that might be received during this time. The system can only detect echoes having a two-way travel time greater than the time required for the reverberation amplitude to fall below an echo detection threshold.
The distance corresponding to this minimum two-way travel time is called “the blind zone”. In principle, the blind zone represents a minimum detection range inside which the ultrasonic radar system is unable to detect anything. For example, a parking-assist system may employ such ultrasonic radar systems as parking-assist sensors (“PAS”) to monitor the distance between the vehicle and nearby obstacles, but they would be unable to warn the driver of any obstacles so near as to be within their blind zones. Thus it is desirable to minimize the blind zone by minimize reverberation of the transducers. Yet it would be undesirable for such minimization to unduly increase system complexity or cost and thereby undercut the traditional advantages of this system configuration.